1. Field of the Invention
This invention relates to a titanium trichloride useful as Ziegler-type catalyst component. The invention further relates to the method of producing titanium trichloride catalyst component. More particularly, the invention relates to a highly active, highly crystalline shear resistant titanium trichloride which has been prepolymerized with a mixture of propylene and a higher alpha-olefin.
2. Related Art
Pretreatment of Ziegler-type catalysts with alpha-olefins is known in the art and some of the references are noted here. The pretreatment is generally performed in order to stabilize the catalyst. For example, in British Pat. No. 1,300,734 (published Dec. 20, 1972) of Shell International Research Maatschappij N.V., it is taught that by contacting a Ziegler-type catalyst comprising a titanium halide and an organoaluminum compound with a small amount of an alpha-olefin a stabilized catalyst is obtained. By "stabilization", the patent teaches that reduction of catalytic activity during polymerization reaction does not occur such that the overall activity is maintained at a high level.
In accordance with British Pat. No. 1,384,063 of Shell International Research Maatschappij N. V., there is disclosed a titanium halide aluminum trialkyl polymerization catalyst which is stabilized against deterioration during the polymerization reaction by prepolymerizing the catalyst at a temperature below 62.degree. C. prior to its being employed in the conventional polymerization reaction.
In the British Pat. No. 1,408,611 (published Oct. 1, 1975) of Shell International Research Maatschappij N. V. there is disclosed the preparation of a titanium trichloride catalyst component which involves reducing titanium tetrachloride to a beta-type titanium trichloride, activating the titanium trichloride to a gamma titanium trichloride and thereafter contacting the same with propene in order to form a prepolymerized catalyst component.
In U.S. Pat. No. 3,404,096 of Lamborn, issued Oct. 1, 1968, there is disclosed a method of pretreating Zeigler-type catalysts with ethylene so as to form curdy catalyst component which is useful for obtaining friable fine catalyst particles.
In U.S. Pat. No. 3,689,597 of Mahlman, issued Sept. 5, 1972, there is disclosed a method of obtaining fine polypropylene particles by polymerizing propylene in the presence of a titanium trichloride catalyst which has been pretreated with alpha-olefins.
In U.S. Pat. No. 4,309,521, the titanium trichloride reduction product is activated for use as a polymerization catalyst by pretreating with an alpha-olefin or mixture of alpha-olefins.
In U.S. Pat. No. 4,325,837, a reduction in catalyst fines is achieved by prepolymerizing an aliphatic mono-1-olefin having 2 to 10 carbon atoms to provide a 1-50 weight percent prepolymer based on the total weight of the composition.
UK Patent Specification No. 1,135,697 discloses preparing fine catalyst particles for preparing fine particles of polyolfins by pretreating trivalent titanium precipitate with a straight-chain alpha-olefin or mixture thereof having 8 to 16 carbon atoms. By using 1 to 2.5 moles per mole of titanium of the alpha-olefin, the catalyst particles are fractured, i.e., highly friable.
The method of preparing the reduced titanium trichloride product which is employed in the prepolymerization of the present invention and the method of activation of the prepolymerized catalyst product do not form a part of the present invention and any of those methods disclosed in the art may be employed, although some particular methods are preferred.
Similarly other treatments such as that disclosed in U.S. Pat. No. 4,330,433 for producing large size catalyst may employ the present invention to produce stabilized catalyst of the large size. Briefly, that patent discloses a procedure for producing titanium catalyst by reducing titanium tetrahalide under controlled conditions of temperatures, reduction rate and concentrations to produce reduced titanium halide solids product seeds having an average particle size dimater of about 20 microns or greater and thereafter simultaneously and without interruption adding to the seeds containing system titanium tetrahalide and organometallic reducing compound at a rate to reduce the titanium tetrahalide to titanium trihalide of about 6.times.10.sup.-4 to about 0.02 milli-moles per liter per second per meter.sup.2 of available preformed titanium trihalide surface area until a solids product of desired size is obtained. The resultant product may be stabilized according to the present prepolymerization process.
The reduction of titanium tetrachloride is well documented in the art and described in numerous references and patents. Generally the titanium trichloride-containing compound is obtained by reducing titanium tetrachloride with an organoaluminum compound, preferably an alkylaluminum halide. For example, U.S. Pat. Nos. 4,085,064; 4,062,804; 4,172,514; 4,127,505; 4,182,691, and 4,210,738 disclose the general procedure and/or specialized variations thereon.
Several methods describing the activation of titanium trichloride obtained by low temperature reduction of titanium trichloride with an organoaluminum compound are described in the published patent literature. The activation is generally accomplished by contacting the reduction product of titanium tetrachloride with complexing agents and with various halogenated compounds to obtain a purple titanium trichloride which is useful as a cocatalyst with an organo-metal compound for the polymerization of alpha-olefins.
More particularly, in Japanese Patent Application (OPI) No. 34478/1972, published on Nov. 21, 1972 and corresponding to British Pat. No. 1,391,068 there is described a process which comprises treating the reduced solids obtained by low temperature reduction of titanium tetrachloride with an organoaluminum compound with a complexing agent, e.g., an ether, and titanium tetrachloride.
In Japanese Patent Application (OPI) No. 112289/1975, published Sept. 3, 1975, there is described a process wherein the titanium trichloride-containing reduced solids product obtained from the low temperature reduction of titanium tetrachloride in the presence of an organoaluminum compound is treated with a complexing agent, e.g., ethers, and then the resulting brown TiCl.sub.3 -containing catalyst is treated with carbon tetrachloride.
Additionally, in Japanese Patent Application (OPI) No. 143790/1975, published Nov. 19, 1975, a method is described comprising treating the reduced solids product with a mixture of a complexing agent and carbon tetrachloride.
In Japanese Patent Application (OPI) No. 149897/1976, published Dec. 23, 1976 and corresponding to British Pat. No. 1,484,086, there is described a process in which brown titanium trichloride obtained from the reduction of titanium tetrachloride in the presence of an organoaluminum halide and at low temperatures is subjected to heat treatment in the presence of a halogenated aliphatic or aromatic hydrocarbon in order to produce a violet titanium trichloride. It is further disclosed that the brown titanium trichloride obtained from the reduction step may be treated with a complexing agent, including ethers, prior to heat treatment.
In Japanese Patent Application (OPI) No. 227/1977, published Jan. 5, 1977, there is described a process which comprises heat-treating the reduction product of titanium tetrachloride with an organoaluminum compound, treating the reduced solid with a complexing agent and then treating the resulting solids with an alkylaluminum dihalide or titanium tetrachloride.
Furthermore, in U.S. Pat. No. 3,825,524 there is described a process for the production of titanium trichloride catalyst having a high activity which includes contacting a crude titanium trichloride composition, obtained by reducing titanium tetrachloride with an organoaluminum chloride, with a mixed solvent system composed of (i) a main solvent of aliphatic or aromatic hydrocarbons, aromatic chlorinated hydrocarbons or trichloroethylene, and (ii) an auxilliary solvent, including ethers. The mixed solvent system is employed for the purpose of extracting undesirable components from the reduction product.
In Japanese Patent Application Publication No. Sho. 52-142691, of Chisso Corp., published Nov. 28, 1977, there is described a method of producing a titanium halide catalyst component wherein a small amount of propylene is present during the preparation of the titanium halide obtained during the reduction of titanium tetrachlorie with an organoaluminum compound and thereafter treating the obtained reduced solid with a Lewis acid and/or a complexing agent.
In U.S. Pat. No. 4,295,991, there is disclosed the preparation of a titanium trichloride catalyst component which involves a low temperature reduction of titanium tetrachloride with an organoaluminum compound, treating the resulting reduced solids product with an alpha-olefin to obtain a non-friable prepolymerized reduced solid which can thereafter be activated with a halogenated hydrocarbon and a Lewis base or TiCl.sub.4 and a Lewis base.
It is well known that during the formation of polyolefin particles obtained in the presence of transition metal halide catalysts, such as titanium halides, the polymer particles are essentially replicates of the catalyst particles. It is further known that during the activation of the titanium halides obtained from the low temperature reduction of titanium tetrachloride that the transition metal halide particles are friable, i.e., they will shear into smaller particles, i.e., fines. Therefore, it is highly desirable to obtain transition metal halide catalyst components which are essentially non-friable during activation and when subjected to mechanical shearing forces which may occur either during activation or polymerization.